The invention relates to a forming roller for a machine for manufacturing moulded bodies with the rotary-die method and a method for processing such forming rollers, with the features of the indroductory part of the independent patent claims.
For a long time it has been known to manufacture moulded bodies such as for example soft gelatine capsules with the so-called rotary-die method. Such a rotary-die method is for example described in EP 227 060.
With this method two tapes forming the raw material for the moulded body are guided through two counter rotating rollers. These forming rollers on their upper surface comprise deepenings which are bordered by webs. The two tapes are heated suitably until below the melting point and are welded to one another by the force effect of the webs. Simultaneouly by way of squeezing, the moulded bodies are separated out from the tapes. Before the welding with a so-called fill-wedge, a filling means may be locally injected between the two tapes. The filling means locally forces the tape regions into the reliefs of the forming rollers provided therefor, by which means the moulded bodies are formed, for example soft gelatine capsules.
The distance between the two forming rollers and the thickness of the material tapes to be connected determines essentially the force acting on the material tapes and thus the type and manner of the connection.
The pressure acting on the tape may not be selected infinitely large, since otherwise the edges of the moulded bodies to be manufactured are squeezed or destroyed. The pressure may however neither be selected infinitely small, since otherwise the two tapes are not sufficiently connected to one another.
Also when the pressure for connecting the two tapes is sufficient there are problems. On injecting the filling material between the two tapes the tapes are forced into the deepenings on the forming roller. With this there arises the danger that the material tape is not only stretched but also displaced beyond the webs towards the deepenings. This slip of the material tape leads to an irregular, in particular not rotationally symmetric banana-like shape of the manufactured moulded body (so-called bananas or xe2x80x9csmall boatsxe2x80x9d). It is not possible to prevent this slip by way of a higher pressing force of the two forming rollers, since with this the quality of the seam formation between the two tapes would be compromised.
It is therefore the object of the present invention to prevent the disadvantages of that which is known, in particular to provide a forming roller which whilst retaining a high quality of the seam formation and a sufficient seam thickness, avoids the problem of the slip of the material tape.
Furthermore the forming roller is to be manufacturable as simply as possible and in an economical way and manner.
According to the invention these objects are achieved with a forming roller with the features of the latter parts of the independent patent claims.
In the following one forming roller is always referred to. It is clear that with a machine for manufacturing moulded bodies with the rotary-die method two counter rotating forming rollers are applied. The two forming rollers are formed mirror imaged in the same manner.
The forming roller according to the invention comprises a surface which is provided with a multitude of deepenings for receiving the moulded body to be manufactured. The moulded body is forced into these deepenings by injecting the filling material. Two tapes of raw material for manufacturing the moulded body are guided through between two counter rotating forming rollers.
The deepenings are surrounded by webs projecting beyond the surface of the forming roller. The webs press the two tapes, for example gelatine tapes, against one another and connect these each along a closed line.
For preventing slip of the material webs the surface of the forming roller in the region of the webs comprises at least one partly roughened surface. By way of the roughening of the surface, in particular on the web surface, the friction adhesion between the surface of the forming roller and the tapes is increased, by which mean the slip is reduced.
Here and in the following, roughened means that the surface in comparison to a surface of known forming rollers has a larger roughness. In particular roughened means a surface with a roughness with values Ra larger than 1.0 xcexcm.
Such a forming roller is furthermore also particularly economically manufacturable. By way of this the polishing of the surface of the forming roller necessary until know is done away with.
The web surface runs roughly parallel to the surface of the forming roller and is advantageously roughened over its whole surface. In the region of the web surface the material tape bears on the surface of the forming roller, by which means a particularly good improvement of the adhesion is achieved.
In an advantageous embodiment example also the outer surface of the webs, which is approximately perpendicular to the surface, may be roughend over its whole height. Further also the surface lying outside the webs may be roughened at least in a region neighboring the outer surface of the webs.
The deepening lying within the webs further comprises an inner wall which at least in an edge region connecting to the web surface runs roughly perpendicular to the surface and is roughened. With such a geometry the slip is additionally reduced.
For reasons of manufacturing technology under circumstances it is particularly simple when the whole surface is roughened. The whole surface in this context is to be understood as the surface of the webs and the surface lying between the webs. It is however not necessary to completely roughen the deepenings.
For example with pot-shaped deepenings the moulded body to be manufactured only comes into contact with the surface of the deepening in the edge regions lying neighboring to the web surface. The surface structure of the deepening in a lower region of the inner wall and in the floor region is therefore of a lesser importance with regard to the slip.
In a preferred embodiment example the webs further comprise an inner bevelling arranged between the web surface and the inner wall of the deepenings. The bevelling permits a more gentle stamping of the moulded bodies out of the two tapes connected to one another, by which means the quality of the seam formation may be improved. The bevelling does not need to be roughened.
The type and size of the roughness of the roughened surface regions of the forming roller in particular depends on the type of the applied material. It has been shown that with the manufacture of soft gelatine capsules with gelatine tapes, a roughened surface with an arithmetical means roughness value Ra of 1.0 to 2.0 xcexcm, preferably 1.4 to 1.7 xcexcm is particularly advantageous. The roughened surface has additionally advantageously about 150 to 250 peaks/cm (Pc). Roughness characteristic dimensions here and in the following are specified according to DIN 4760-65.
The surface of a forming roller for a machine for manufacturing moulded bodies with the rotary-die method in a method according to the invention is subjected to a treatment by a granular blast means and with this is roughened. It is of course possible to apply other mean and methods for producing roughened surface structures. For the application of forming rollers in the manufacture of soft gelatine capsules it has been shown that a blast means with a granulation of 0.2 to 0.1 mm and with an approximately round shape or irregular break leads to a particular advantageous roughness. In particular corundum, glass or sand may be applied.
The surface of the forming roller may be particularly simply processed in that the forming roller is rotated on a rotating device at about five to ten rev/min. and at the same time impinged with a blast means. Advantageously the blast means is blasted from at least one injector nozzle against the surface of the forming roller, wherein the injector nozzle is moved parallel to the forming roller and runs up the whole roller surface.
In a further preferred embodiment example the blast means is blasted against the surface of the forming roller by way of two injector nozzles standing at an angle to each other.